J . Am. Chem. SOC.1990, 112, 6092-6094
6092
First Structural Study of a Thiophosphorane Containing a Six-Membered Ring. Phosphorus-Sulfur vs P hosphorus-Oxygen Ligand Preferences ,* K. C. Kumara Swamy, Joan M. Holmes, Roberta 0. Day, and Robert R. Holmes* Contribution from the Department of Chemistry, University of Massachusetts, Amherst. Massachusetts 01003. Received September 15, 1989. Revised Manuscript Received March 31, I990
Abstract: Oxidative addition of phenanthrenequinone to the newly synthesized dithiaphosphorinane, (Xylyl-O)P-S(CHJ3S ( l ) , results in a new thiophosphorane containing a sulfur-bonded six-membered ring. X-ray analysis on separate crystals reveals both a monoclinic and triclinic modification. This represents the first structural study of a six-membered ring containing thiophosphorane. The structure which is a trigonal biyramid has the ring sulfur atoms located in apical-equatorial sites instead of the expected diequatorial arrangement. As a consequence, the more electronegative xylyloxy oxygen atom is relegated to an equatorial position. A slightly twisted boat conformation exists for the dithiaphosphorinane ring. 'HNMR spectroscopy is consistent with the retention of the solid-state structure in solution which undergoes rapid intramolecular ligand exchange.
Although an abundance of structural studies indicating conformational preferences for phosphoranes containing five-membered rings has been performed,'~~ little is known about corresponding six-membered ring systems.5 In the case of analogous thiophosphoranes, no structural information appears to be available.6 I n this paper we report the first structural study of an unusual thiophosphorane containing a six-membered phosphorinane ring with ring sulfur atoms bonded to phosphorus. It is obtained in both a triclinic form, 2A, and a monoclinic form, 2B, from the oxidative addition reaction of phenanthrenequinone to 1 (eq I ) , followed by recrystallization from dichloromethane.
+ $0 O
\
( I ) (a) Pentacoordinated Molecules. 80. (b) Part 79: Kumara Swamy, K. C.; Chandrasekhar, V.;Harland, J. J.; Holmes, J. M.; Day, R. 0.; Holmes, R. R. J . Am. Chem. SOC.1990, 112, 2341. (2) (a) Kumara Swamy, K. C.; Burton, S.D.; Holmes, J. M.; Day, R. 0.; Holmes, R. R. Presented in part at the XI International Conference on Phosphorus Chemistry, Tallinn, Estonia, SSR/USSR, July 1989; Abstract 2-22. (b) Burton, S. D.; Kumara Swamy, K. C.; Holmes, J. M.; Day, R. 0.; Holmes, R. R. J . Am. Chem. Soc. 1990.11 2, third of three papers in this issue. (3) Holmes, R. R. Pentacoordinared Phosphoru'sStructure and Spectroscopy; ACS Monograph 175; American Chemical Society: Washington, DC, 1980; Vol. I and references cited therein. (4) Holmes, R. R. Prog. Inorg. Chem. 1984.32, Chapter 2 and references cited therein. ( 5 ) Some X-ray studies of phasphorana with six-membered rings in a boat or twist-boat conformation involving oxygen and nitrogen ring atoms attached to phosphorus are as follows: (a) Barlow, J. H.; Bone, S.A,; Russell, D. R.; Trippett, S.;Whittle, P. J. J . Chem. SOC.,Chem. Commun. 1976, 1031. (b) Schomburg, D.; Weferling. N.; Schmutzler, R. Ibid. 1981,810. (c) Pochlauer, P.; Petter, W.; Peringer, P.; Muller, E. P. Ibid. 1985, 1760. (d) Schomburg, D.; Hacklin, H.; Roschenthaler, G. V. Phosphorus Suljur 1988,35, 241. (e) Yu, J . H.; Bentrude, W. G.J . Am. Chem. SOC.1988,110,7987 ( A report of a non-chair conformation for a six-membered oxygen-nitrogen ring bonded to pentacoordinated phosphorus apically and equatorially based on solution 'H NMR evidence. More recently, these same workers reported a twist conformation for a model system closely related to CAMP: Yu, J. H.; Bentrude, W. G. Tetrahedron Left. 1989, 30, 2195). (6) A report of a phosphorane with a six-membered dithianaphthalene ring system is available but no structural information is given: Kimura, Y.; Kokura, T.; Saegusa. T. J . Org. Chem. 1983, 48, 3815.
X-ray analysis shows that the two crystalline modifications of 2 possess a trigonal-bipyramid structure with the principal difference between them being in the orientation of the 0-xylyl group relative to the remainder of the molecule (Figure 1). Moreover, an apical-equatorial orientation for the sulfur-containing ring in both modifications arises in preference to a diequatorial ring placement that would allow the more electronegative oxygen atom of the xylyloxy group access to its preferred apical location. The observed structure is also unexpected on the basis of relative ring strain effects. In the diequatorial position, the six-membered ring suffers little strain, being accommodated with an ideal angle at phosphorus of 120°, whereas the actual structure contains the ring at a trigonal-bipyramidal angle at phosphorus of 90'. In the monoclinic form, 2B, the intermolecular packing includes stacking interactions between phenanthrene groups of inversion related pairs of molecules (Figure 2). The phenanthrene planes of such pairs, required by symmetry to be parallel, are separated by a distance of 3.524 A. In the triclinic form, 2A, inversion related pairs are in van der Waals' contact via atoms of the six-membered heterocylic rings and no stacking interactions are observed. The packing is apparently more efficient in the monoclinic form as evidenced by the densities: 1.405 g/cm3 for 2B versus 1.346 g/cm3 for 2A. Despite the marked difference in the mode of packing for the two forms, the geometries of the spirocyclic systems are nearly identical and the only important difference in the molecular geometries involves the disposition of the xylyloxy group (Figure I ) . This provides fairly compelling evidence that the apicalequatorial placement of the six-membered ring is in no way due to the energetics of packing, but rather reflects energy minimization within the molecule. A further feature of the two forms of 2 is the presence of the six-membered ring in a near boat (or twist boat) conformation, with the axial sulfur atom, SI,and the opposing carbon atom, C2, at the prow and the stern of the boat (Figure 3). The five-membered ring is essentially planar and coplanar with the fused phenanthrene group (the 17 atom system is coplanar to within f0.059 A for 2B and f0.114 A for 2A). The axial-equatorial orientation for the six-membered ring in a near boat conformation is of the type discussed by TrippettS8v7 for phosphoranes that allows lone pairs of the equatorial ring atoms bonded to phosphorus to be placed near the equatorial plane for effective back-bonding.* The extent to which this effect might occur for sulfur atoms in a derivative of this type is not known with any ~ e r t a i n t y . ~However, the preferred ring stabilization (7) (a) Trippett, S . Pure Appl. Chem. 1974, 40, 595. (b) Bone, S. A.; Trippett, S . : Whittle, P. J. J . Chem. SOC.Perkin I 1977, 80. (8) Hoffmann, R.;Howell, J. M.; Muetterties, E. L. J . Am. Chem. SOC. 1972, 94, 3047.
0002-7863/90/ 15 12-6092$02.50/0 0 1990 American Chemical Society
Study of a Thiophosphorane Containing a Six- Membered Ring
J . Am. Chem. SOC..Vol. 112, No. 16, 1990 6093
pared to the trigonal bipyramid.3~"~12Presumably the presence of the more flexible saturated six-membered sulfur containing ring system in 2 inhibits the formation of a square-pyramidal structure. The IH NMR in CDC13solution by itself does not differentiate between retention of the solid-state structure for 2 undergoing rapid Berry pseud~rotation'~ and a structure having a diequatorial ring orientation. However, variable-temperature N M R studies2~14.'5 on related spirocyciic phosphoranes containing six-membered rings indicates nonrigid molecules with the presence of rapid permutational isomerization occurring at room temperature, e.g., in 4.15
4
A variable-temperature IH NMR study of 2 in CD2Cl2solution showed no significant change in the spectrum down to -90 OC similar to that found for 516and 6.14Here, it was concluded14J6 that a rapid, simple Berry exchange (a-e e a ) was not slowed down to the lowest temperatures studied. By analogy, we presume that this also is occurring in 2 but the N M R data alone are not definitive.
-;p-0 Me
mw
9 Me
5
Figure 1. ORTEP plots showing the solid state molecular geometry of 2 in (a) the triclinic form, 2A, and (b) the monoclinic form, 2B. Bond lengths (A) for 2A,2B: P-01 = 1.746(2), 1.753 (2);P-02 = 1.649(3), 1.645 (2);P-03 = 1.607 (3),1.598 (2);P-SI = 2.151 ( I ) , 2.145 ( I ) ; P-S2 = 2.090 ( I ) , 2.092 ( 1 ) . Bond angles (deg) for 2A,2B: P-SI-CI = 99.4 ( I ) , 99.2( I ) ; P-S2-C2 105.8 ( I ) , 107.6( I ) ; SI-P-S2 = 98.94 ( 5 ) . 97.81(4);SI-P-01 = 176.03 (9),178.62 (7);SI-P-02 = 89.78 (8), 89.92(7);SI-P-03 85.49 (8),86.30(7);S2-P-01 = 84.78(9).83.51 (7);S2-P-03 = 122.4 ( I ) . 123.39(8);01-P-02 = 89.7 ( I ) , 89.76 (8); 01-P-03 91.3 ( I ) , 92.66 (9); 02-P-03 = 120.2 ( I ) , 117.2 ( I ) .
in apical-equatorial sites for 2 is sufficient to override the usual orientation observed for the more electronegative oxygen atom at an apical site of a trigonal bipyramid. It must be pointed out that Trippett's prediction is not universally obeyed, as related work on azoxyphosphoranes has shown.I0 In a somewhat related phosphorane, 3, containing a fivemembered ring, X-ray analysis revealed an entirely different structure, that of a square-pyramidal geometry.I0 Here, ring strain effects for such unsaturated systems support a preference for the normally higher energy square-pyramidal structure com~
~~
(9)An estimate of P-S, bond rotational barrier in a trigonal bipyramid
of about I O kcal/mol has been made.s' (IO) (a) Day. R. 0.;Kumara Swamy, K. C.; Fairchild, L.; Holmes, J. M.; Holmes, R. R., submitted for publication. (b) Holmes, R. R.; Day, R. 0.; Fairchild, L.; Kumara Swamy, K. C.; Holmes, J . M.; Burton, S. D. Presented in part at the 199th National Meeting of the American Chemical Society, Boston, MA, April 1990;INOR 503
MeJO $-
Me 6
In view of the present work on the cyclic thiophosphorane 2 and previous structural s t u d i e ~ ~on* ~related J ~ phosphoranes with oxygen- and nitrogen-containing rings, it is concluded that the boat conformation positioned apically and equatorially in a trigonal bipyramid, energetically, is the generally preferred conformation for saturated six-membered rings in phosphoranes in the absence of perturbing influences, e.g., steric effects, hydrogen bonding,1° and packing effects. It remains to learn the importance of this conformation in intermediates in enzymatic reactions of nucleoside cyclic 3',5'-monopho~phates.'~
Experimental Section Chemicals were obtained from Aldrich, Fisher Scientific, and Alfa and used without further purification. Solvents used were of HPLC grade (Fisher Scientific). Further purification was done according to standard procedures.'* ( I 1 ) Day, R. 0.;Sau, A. C.; Holmes, R. R. J . Am. Chem. SOC.1979,101, 3790. (12)Holmes, R. R. J . Am. Chem. SOC.1975, 97, 5379. (13) Berry, R. S.J . Chem. Phys. 1960,32, 933. (14)Kumara Swamy, K. C.; Day, R. 0.; Holmes, J. M.; Holmes, R. R.
J . Am. Chem. SOC. 1990, 112, second of three papers in this issue. ( 1 5 ) Kimura. Y.;Kokura, T.; Saegusa, T. J . Urg. Chem. 1983,48, 3815. (16) Holmes, R. R.; Kumara Swamy, K. C.; Holmes, J. M.; Day, R. 0.
Submitted for publication. (17)(a) Miller, J. P. In Cyclic 3',5'-Nuc/eotides: Mechanisms of Action; Cramer, H., Schultz, J., Eds.; John Wiley and Sons: New York, 1977;pp 77-104. (b) Van 001,P. J. J. M.; Buck, H. M. Eur. J . Biochem. 1982, 121, 329 and references cited therein.
6094 J . Am. Chem. Soc., Vol. I 12, No. 16. I990
Kumara Swamy et al. (6.3 g, 85%): 'H N M R (CDCI,, ppm) 2.00-2.50 (m,CHIC, 2 H), 2.42 (s, CH,, 6 H), 2.65-2.85 (m.CHIS, 2 H), 3.55-3.80 (m, CHIS, 2 H), 6.90-7.10 (m, HA,, 3 H). 31PN M R (CDCI,, ppm) 150.45. anal. Calcd for C I , H I 5 O P S 2 :C, 51.13; H, 5.81. Found: C, 50.44; H, 5.80.
Preparation of (Phenanthrenediyl-9,lO-dioxy)(2,6-dimethylphenoxy)(propanediyl-1,3-dithio)phosphorane, (CI4HBO2) ( Xylyl-O)p[S2(CH,),] (2). 1 (1.82 g, 7.03 mmol) and phenanthrenequinone (1.47 g, 7.03 mmol) were heated together at 145 "C for 15 min under a nitrogen
Figure 2. ORTEP plots showing the stacking interaction in the monoclinic form, 2B viewed parallel to the stacked planes.
atmosphere. After cooling, the solidified mass was dissolved in dry dichloromethane (150 mL) at ca. 35 "C. Crystallization occurred upon slow evaporation of the solvent at 20 " C under nitrogen (IO h) to yield 2 (2.00 g, 61%). The triclinic form, 2A,was obtained from the latter crop of crystals, mp 213-217 "C. A portion of this material (0.5 g) was recrystallized again from dichloromethane (80 mL) over a 48 h period. The monoclinic form, 2B, was obtained from this crop of crystals, mp 208-213 "C. A mixture of 2A and 2B melted over the range 150-205 OC. The same proton N M R spectrum resulted from each: ' H N M R at 20 "C (CDCI,, ppm) 1.93 (m, 2 H, CH2CH2;shows an AB quartet upon decoupling from CHIS protons, 2J(H-H),,inal = -14 Hz), 2.33 (s, 3 H, CH,), 2.34 (s, 3 H, CH,), 2.99 (m,CHIS (A), 2 H), 3.38 (m, CHIS (B), 2 H) (upon decoupling C H 2 S protons from CHIC protons, a four line pattern with equal intensity for each of CH,S (A) and C H 2 S (B) was observed. This pattern has been analyzed for 3J(P-SCH2 (A)) = 35.4 Hz, 'J(P-SCH2 (B)) = 25.2 Hz, 2J(CH2S (A)-CHZS (B)) = -13.5 Hz), 6.86 (br, H(phenoxy), 3 H), 7.45-7.60 (m,H (Ar), 4 H), 7.75-7.85 (m, H (Ar), 2 H), 8.55-8.65 (m,H (Ar), 2 H); "P N M R ((36, ppm) 3.96 (,J(P-H(av) = 31.2 Hz). Anal. Calcd for C2,H2,03PS2: C, 64.38; H, 4.93. Found: C, 64.23; H, 4.89. X-ray Study. Crystals were mounted in thin-walled glass capillaries and sealed. C25H,,03S2P: triclinic form 2A,colorless crystal (0.33 X 0.48 x 0.50 mm), space group Pi,a = 10.008 (6) A, b = 10.149 (4) A, c = 12.166 ( 5 ) A,a = 81.99 (3)", /3 = 87.19 (4)", y = 70.17 (4)". Z = 2,fiMoK~= 3.132 cm", V = 1151.1 A', D, = 1.346 g/cm'; monoclinic form 2B,colorless crystal (0.43 X 0.50 X 0.50 mm), s ace group P2,/n, a = 10.083 (3) A, b = 8.563 (3) A,c = 25.885 (6) 0 = 99.19 (2)", Z = 4,fiMoKa = 3.268 cm-l, V = 2206.3 AS,D, = 1.405 g/cm3. Data were collected on an Enraf-Nonius CAD4 diffractometer (23 f 2 "C, graphite monochromated Mo Ka radiation, X = 0.71073& 0 - 20 scan = 50" (+mode).20 For 2A, 20,,, = 43" (+h,ik,hl). For 2B, 24,, h,+k,il). The structures were solved by direct methods and difference Fourier techniques and were refined by full-matrix least-squares (function minimized Ew(lFoI - lFc1)2,where w ' / * = 2FoL,/a,, independent nonhydrogen atoms anisotropic (3 l ) , independent hydrogen atoms fixed isotropic(23)). The final agreement factors were as follows: 2A, R = 0.041, R, = 0.057 for the 2085 reflections having I > 3aI; 2B,R = 0.037 and R, = 0.055 for the 2950 reflections having I > 3 q .
A),
Figure 3. ORTEP plot showing the twist-boat conformation of the sixmembered ring in 2A. The ring conformation in 2B is very similar. ' H and "P N M R spectra were recorded on a Varian X L 300 FT/ N M R spectrometer equipped with a multinuclear broad-band probe and operated at 300 and 121.4 MHz, respectively. Resonances are referenced versus tetramethylsilane ('H) and 85% orthophosphoric acid (external standard, ,IP). Preparation of 2-(2,6-Dimethylphenoxy)-1,3,2-dithiaphosphorinane,
.
(Xylyl-O)P-S(CH2),S ( I ) . To a solution of 2-chloro-l,3,2-dithiaphosphorinane (4.94 g, 28.6 mmol) (prepared from phosphorus trichloride, 1,3-propanedithiol, and triethylamine in diethyl ether and purified by distillation in vacuo: (,lP N M R 6 = 136.7 ppm; lit.'9 6 139.7 ppm) and 2,6-dimethylphenol (3.50 g, 28.6 mmol) in diethyl ether (1 50 mL) was added dropwise a solution of triethylamine (3.1 g, 30 mmol) in diethyl ether ( 1 5 mL) over a period of 20 min with continuous stirring at 0 "C under a nitrogen atmosphere. The mixture was stirred overnight and filtered under nitrogen. Diethyl ether and excess of triethylamine were distilled off, and the residue was redissolved in diethyl ether (50 mL) and filtered. The solvent was removed completely to obtain the new compound, 2-(2,6-dimethylphenoxy)-l,3,2-dithiaphosphorinane( l ) ,as an oil ( I 8) Vogel, A. I. Textbook of Practical Organic Chemistry; Longman: London, 1978. (19) Martin, J.; Robert, J. B.; Taiele, C. J . Phys. Chem. 1976,80, 2417.
Acknowledgment. The support of this research by the Army Research Office (Grant DAA03-88-K-0190) and the National Science Foundation (Grant CHE-8819152) is gratefully acknowledged. Supplementary Material Available: Figures of the ORTEP plot showing the twist-boat conformation of the six-membered ring in 2B, the ORTEP plot showing the stacking interaction in the monoclinic form, 2B, viewed perpendicular to the stacked planes, (Figures SI and S2, respectively), atomic coordinates, anisotropic thermal parameters, hydrogen atom parameters, and bond lengths and angles for 2A (Tables SI-S4,respectively) and for 2B (Tables S5-S8, respectively) (18 pages). Ordering information is given on any current masthead page. (29) Details of the experimental procedures have been described previously: Sau. A . C.; Day, R. 0.;Holmes, R. R. fnorg. Chem. 1981, 20, 3076.
